Fault injection with the existing host fakes for FixedPatchStepper(
refinements=[]): an initialize upload failure, a BlockHaloCopy,
BlockCurvedBoundary or BlockStep launch failure, and a failing final
stream wait each raise, leave the instance failed (step/download refused)
and keep the completed step count; a failed launch never reaches the wait.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Review follow-ups for S1 (f764d68):
- a single level starts its spare buffer NaN, as PeriodicBlockStepper does,
so stale halos cannot hide (multilevel initialization unchanged);
- projected explosion is rejected for a single level;
- new tests/unit/test_single_level.py: NaN spare after initialize, per-step
launch order halo -> BFL (circles only) -> BlockStep with a null kind and
one wait per step(n), circle solids excluded from the state mask;
- the GPU bitwise comparison also covers shifted storage.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
